Hitherto, copolymers containing a unit derived from a polyfluoroalkyl group-containing polymerizable monomer are widely used as a water- and oil-repellent agent. In order to obtain the polyfluoroalkyl group-containing copolymer, a polymerization method such as a bulk polymerization, a solution polymerization, a suspension polymerization and an emulsion polymerization can be used. Generally, the solution polymerization and the emulsion polymerization are used. Among them, an aqueous emulsion prepared by the emulsion polymerization is industrially advantageous over a solvent dispersion prepared by the solution polymerization, in view of a work-environmental problem and an effect on environment.
In the emulsion polymerization for obtaining the aqueous dispersion of the polyfluoroalkyl group-containing copolymer, it is known that a polyfluoroalkyl group-containing polymerizable monomer is extremely water-insoluble and a reaction in a dispersion medium consisting of water can hardly proceed. Thus, a method of using a ketone and glycol organic solvent as an auxiliary solvent have been conventionally proposed for the purpose of improving the solubility. Even if, however, the aqueous dispersion is used, the use of a low flash point solvent such as acetone has a problem of product combustibility and the use of a high flash point solvent has the problem caused by an organic solvent that the environmental deterioration such as air pollution and waste water pollution are caused during processing.
Recently, a method of obtaining an aqueous dispersion of polyfluoroalkyl group-containing copolymer without using the auxiliary solvent is proposed for the purpose of solving the above-mentioned problems. For example, in JP-A-4-248863 and JP-A-11-255995, although a special emulsifier such as a fluorine-containing amine oxide and a betaine type surfactant is used as an emulsifier, the improvement of stability is inadequate and the water- and oil-repellency is also inadequate. Although, in JP-A-5-17538, JP-A-6-49319 and JP-A-9-291481, the copolymerization of hydrophilic monomers having a COOH group, an OH group or a polyoxyethylene group is carried out to improve the stability, the polymer has small fluorine content so that water- and oil-repellency is inferior. Although, in JP-A-6-166705, a solution polymerization is conducted to prepare an aqueous dispersion which is then subjected to a desolvent process, a manufacturing method is not simple and the improvement of stability is insufficient. JP-A-2000-160149 and JP-A-2002-530443 are still insufficient in stability, although some of above-mentioned problems are improved. Although, in WO02/24828, the improvement of stability is intended by adding a hydrophilic surfactant after the emulsification step using a hydrophobic surfactant and before the polymerization step, it is necessary to add the emulsifier in the course of a manufacturing process so that a manufacturing method is not simple. In these procedures proposed, a compound having a large specific gravity is used as a polyfluoroalkyl group-containing polymerizable monomer, and the sedimentation stability of the aqueous dispersion is poor during the emulsification and after the polymerization because of use of said compound.
On the other hand, in WO02/083809 and WO03/062521, the water- and oil-repellency is inadequate, although the water- and oil-repellent composition comprising a short chain Rf group is disclosed. Although the use of a solvent is not indispensable, said publications do not have a disclosure about the composition excellent in both of the water- and oil-repellency and the stability without using the solvent, and said publications exclusively have working examples comprising the solvent. The composition, which is manufactured in accordance with the method described in the working examples except the solvent is not used, has inadequate water- and oil-repellency, and also inadequate stability.
Thus, in the conventional arts, the aqueous water- and oil-repellent dispersion simultaneously exhibiting high water- and oil-repellency and excellent storage stability with the absence of a solvent has not been obtained.